The invention relates to a sliding-tongue compound needle for a knitting machine comprising a needle equipped with a hook and a sliding tongue at least partially straddling the needle and equipped with at least one butt, with an end and with a shoulder, the bottom of this sliding tongue being longitudinally slotted in its distal region comprising the end and the shoulder so as to allow the end to be parted, by the needle or by an opposed needle or an opposed sliding tongue, the sliding tongue being movable relative to the needle so as to close and open the hook of the needle and so as to drive a stitch along via its shoulder.
A needle such as this is described in Patent Application EP 0 881 315, filed by the Applicant, the content of which is incorporated by reference hereto. In the embodiment described in that document, the bottom of the sliding tongue and the upper edge of the needle are rectilinear and parallel to the direction of travel of the needle. Movement of the sliding tongue is therefore also rectilinear and parallel to the direction of travel of the needle. Because of this configuration, when the needle advances relative to the sliding tongue to come into the position for preparing to transfer a stitch, the stitch that is to be transferred has to ride up a ramp on the needle until it is practically level with the bottom of the sliding tongue. This has the effect of exerting upward tension on the stitch and has the result of enlarging the stitch. This effect is further reinforced when the sliding tongue advances, carrying the stitch over the hook of the needle, the end and the shoulder of the sliding tongue passing very much over the hook of the needle. The fineness of the stitches that can be knitted is therefore limited.
In a compound needle of the conventional earlier type, that is to say in which the needle, in the form of a slider, equipped with a needle hook, lies under a slideway that closes and opens the hook, it has been proposed, in Patent FR 2 652 593, the content of which is incorporated herein by reference, that means be provided for raising and lowering the slideway relative to the bottom of the slot of the needle so as to reduce friction and tension on the stitch carried by the needle and obtain more even stitches. These means consist, on the one hand, of a bearing effect in the bottom of the slot of the needle and, on the other hand, of a lever effect exerted by the needle push rod. The path of the end of the slideway is not, however, governed tightly enough and, what is more, because of the general design of the needle, the slideway cannot move beyond the hook of the needle but merely moves back and forth between a lowered position and a raised position relative to the bottom of the sliding tongue.
The object of the present invention is therefore to allow the knitting of finer and more even stitches and, in addition, to make the transfer of stitches to one or more receiving elements easier.
To this end, the sliding-tongue compound needle according to the invention is one which has means for the positioning and vertical guidance of the sliding tongue in all positions of the sliding tongue as it moves relative to the needle, these means for the guidance and vertical positioning consisting exclusively and wholly of special shapes of the needle and of the sliding tongue and such that the sliding tongue moves along a nonrectilinear path controlled at all points and having rising and falling movements.
By guiding the sliding tongue in a perfectly controlled way, these guide means have the effect of reducing as far as possible the vertical tension on the stitch and therefore its enlargement. It is thus possible to knit finer and more even stitches.
According to a preferred embodiment of the invention, the bottom of the sliding tongue is open between the butt and approximately the middle of the sliding tongue, and the needle has an arm extending from the rear forward roughly parallel to the body of the needle, this arm passing through the sliding tongue via its open bottom to extend over the solid part of the sliding tongue so as to form, with the body of the needle, a fork in which the sliding tongue is guided.
To provide guidance, the internal dimensions of said fork and the bottom and back of the solid part of the sliding tongue are advantageously in the shape of cams providing the nonrectilinear movement of the sliding tongue, that is to say causing it to rise and fall relative to the needle.
According to one embodiment, the sliding tongue has, at the rear, at least one bearing point collaborating with the body of the needle to prevent inadvertent rocking of the sliding tongue and/or to induce a movement of the rear of the sliding tongue in a vertical plane relative to the needle. In this last instance, at least one of the sides of the needle body against which the bearing point rests, is in the form of a cam.